The invention relates to a fluid friction clutch.
Fluid friction clutches are known for the most various fields of application. Usually a fluid friction clutch comprises a clutch input part drivable about a rotation axis, a clutch output part rotatable coaxially in relation to the clutch input part, which together with the clutch input part defines at least one shear gap, and a cover the cavity of which, enclosing at least the region of the shear gap, is filled partially with viscous fluid and otherwise with air.
From U.S. Pat. No. 3,400,796 a fluid friction clutch is known the shear gap width of which is variable for the control of the force transmission. From German Publ. Spec. No. 3,419,927 a fluid friction clutch is known which is formed as by-pass clutch in a hydrodynamic torque converter. Finally from German Utility Model No. 8,235,536 a fluid friction clutch for a cooling air fan of an internal combustion engine is known, in which the transmitted torque is controllable in dependence upon temperature
The silicone oil used in such fluid friction clutches as viscous fluid is thermally stressed in operation. The thermal overloading of the viscous fluid reduces the life of the fluid. This is the case especially if high demands are made on the torque transmission capacity of the viscous fluid. The thermal loading of the viscous fluid could per se be reduced by the use of larger and thus more powerful fluid friction clutches. In most practical cases however this is not possible for reasons of space, weight and cost.
Now the invention is directed towards provision of a fluid friction clutch in which the viscous fluid has a comparatively long life even in the case of increased thermal loading.